Storage tanks are widely used for storing a variety of liquids. Some of these liquids are hazardous and can be corrosive and/or flammable. In particular, underground storage tanks are used extensively for the storage of liquid gasoline at retail gasoline stations. The service life of a storage tank will vary, but eventually the tank and its piping will leak. Leaks from the tank system often happen within a few years after the new tank and piping are installed, due to improper insulation or flaws in the manufacturing of the tanks and piping.
Known leakage problems are particulary troublesome in that gasoline storage tanks are usually buried underground. Any leaks which develop are normally very slow initially and are very difficult to detect. Underground storage tanks are susceptible to damage in those area that are prone to earthquakes and winter frost heaves of the ground surrounding the tanks. Typical underground storage tanks are constructed with structural accessories such as a manhead, its lid, and piping for filling, dispensing, and venting. The accessories described are examples of structures which liquids and vapors flow through and all of which are normally located at the top of the tank. Leaks from subterranean tanks or the accessories can result in a significant danger to the environment and health of nearby residents. Federal as well as local regulations govern the design and maintenance of such storage tanks.
Heightened public awareness of the danger posed by underground storage tanks has led to additional governmental regulations. Recent proposed regulations will require most storage tanks to have secondary containment means and possibly a fail safe leak detection design feature to guard against accidental soil and water contamination. Secondary containment is accomplished by a jacket completely encasing the tank and structural accessories. The tank and related accessories are referred to as the primary containment system. Any jacket or wall encasing the primary system is often referred to as a secondary containment system.
Leak detection means are often utilized to monitor the space between the primary and secondary containment systems for leaks or failures. Leak detection devices such as probes or degrading monitoring cables which are utilized to detect gasoline, vapors or water can not detect the failure of the exterior jacket. When the underground jacket fails and there is no ground water present, probes or degrading monitoring cannot detect jacket failures. Probes and degrading monitors are examples of the type monitors that cannot provide a fail safe leak detection means.
The problem associated with inadequate detection means is that when the liquid stored within the primary containment system leaks, the liquid may also leak out of the secondary containment jacket which may have failed in prior years. Also a slow leak from the primary containment may never reach the location of a non fail safe detection device because the liquids leaked from the primary containment into the jacket could drain out of the defective jacket at a location away from the monitors. The best feature of a fail safe detecting means is the continuous monitoring method that establishes the system to be free of leaks, from the time the system is installed to the time the system is removed.
There now has been discovered a total secondary containment system capable of encasing the liquid storage underground tank and tank's structural accessories. The present invention solves the problems inherent with existing tank systems with provisions for leak detection means.